The present invention relates to an image scanner, and more particularly relates to an image scanner used for a digital copier by which inverse images can be obtained.
In a conventional digital copier, inverse images are obtained by reversing luminance data.
FIG. 9 is a block diagram showing an image scanner having a negative-positive inversion function which is used in a conventional digital copier.
In the image scanner illustrated in FIG. 9, image signals are processed as follows: a color-separated document image obtained by the optical system 1 is formed on the image sensors 2; color component signals sent from the image sensors 2 are color-separated by the color separator 10 into luminance data indicating the luminance level, wherein color codes showing red, blue, white and black are added to the luminance data; the color codes of luminance data are ghost-compensated by the ghost compensator 20; the above-described luminance data is compensated by MTF compensator 30 so that the luminance level can be compensated; and the luminance data is .gamma.-compensated by the .gamma.-compensator 50 in order to generate color density data. Further, this image scanner is provided with the marker detector 60 and the luminance data inverter 40, wherein the marker detector 60 detects a red or blue marker from the color codes to which luminance data is added and generates a pulse signal which shows the inverse portion in one scanning line, and wherein the luminance data inverter 40 inverts the luminance data corresponding to the above-described pulse signal.
However, in the above-described image scanner, when a document image is negative-positive inverted, the luminance data is uniformly inverted according to the pulse signal sent from the above-described marker detector 60, regardless of the background density level of the document image, so that a clear inverse image can not be obtained in the case of a document image having a high density background level such as a newspaper.
With reference to the conventional problems described above, the primary object of the present invention is to provide an image scanner which can obtain an inverse image of high gradation even when an image on a high density level background is scanned.